The subject matter disclosed herein generally relates to the field of gear pumps, and more particularly to an apparatus and method for reducing cavitation in gear pumps.
In one example of a gear pump, aircraft gas turbine engines receive pressurized fuel from gear-type fuel pumps. The gear pump typically performs over a wide operational speed range while providing needed fuel flows and pressures for various engine performance functions.
Gear pumps often comprise two coupled gears of similar configuration and size that mesh with each other inside an enclosed gear housing. A drive gear may be connected rigidly to a drive shaft. As the drive gear rotates, it meshes with a driven gear thus rotating the driven gear. As the gears rotate within the housing, fluid is transferred from an inlet to an outlet of the gear pump. Typically, the drive gear carries the full load of the gear pump drive or input shaft. The two gears may operate at high loads and high pressures, which may stress the gear teeth.
For given gear sizes the volume of fluid pumped through the gear pump may partially depend on the geometry of the tooth (e.g., depth, profile, etc.), the tooth count, and the width of the gear. Larger volumetric output may be achieved when lower gear tooth counts with large working tooth depths and face width are used. Alternatively, higher volumetric output may be achieved with higher rotational speed of the pump. Most gear pumps have gears with about ten to sixteen teeth. As the gears rotate, individual parcels of fluid are released between the teeth to the outlet. A common problem with more traditional gear pumps operating at high rotational speeds is cavitation erosion of the surfaces of the gear teeth and bearings. Cavitation erosion results in pitting of surfaces of the gear teeth that may eventually result in degraded pump volumetric capacity and affect pump operability and durability.